I don't understand how this is supposed to be insulting. He's never watched anime obviously but it's probably not his fault why should we care. At least he's like "oh neat" instead of "******* weaboos".

Indeed, you can talk in your own language against a Dutch person and visa versa and both sides will understand most of it. Als German is an easy language for me and I can still speak it at a decent level of course I need to think somewhat longer about what I want to say than in English . Dutch seems really hard to pronounce for people who don't speak Dutch.